Anaerobic Digestion Coupled with Anammox Treatment for Nutrient Retention and Water Quality Improvement

Confined animal feeding operations often use pit recharge waste management systems, where water is recycled from treatment lagoons to flush waste from animal housing. This practice has been linked to reduced animal performance and excess mortality due to the presence of pathogens and ammonia. As a project to improve the quality of flush water, the effluents from two anaerobic digesters were treated in aeration–recirculation systems, one inoculated with an anammox (anaerobic ammonia oxidation) consortium and the other left uninoculated. The effluent from the aeration tanks was sent to a shared constructed wetland planted with cattails and duckweed and hence to a lagoon. Water from the lagoon was recycled back to the digesters, where it was reused to suspend waste for anaerobic digestion. Fresh water was used to suspend feed to the system for the first six months, whereas lagoon water was recycled into the system for the last year and a half. The inoculated aeration tank reduced ammonium concentrations more efficiently than the uninoculated tank and also performed nitrification more effectively. Ammonia oxidation and denitrification continued in the wetland and the lagoon, and ammonium concentrations in the recycled water were reduced by over 98 percent compared to its concentration in the digesters. Phosphate concentrations in the lagoon averaged only 5 percent that of its concentration in the digesters over the two-year evaluation period. Inductively coupled plasma spectroscopy of wastewater sludge and plants showed that chemical precipitation of phosphate and utilization by duckweed and cattails accounted for phosphorus reduction by the system. Wastewater pH, conductivity, chemical oxygen demand and oxidation reduction potential were steady during the study period.